1. Field of the Invention
The invention relates to an improved process for carrying out oxidation reactions on silver foil at temperatures much lower than typically used, and, more specifically, this invention relates to an improved process for the production of formaldehyde, ethylene oxide, propylene oxide, and phenol at room temperature.
2. Background of the Invention
The reaction of methanol to form formaldehyde is a large-scale industrial process carried out over silver or copper catalysts. The 1997 worldwide production was in excess of 1.5×107 tons. Due to its commercial importance, this reaction has been studied extensively in efforts to improve the efficiency of the process and to understand the reaction on a molecular basis.
Under oxidizing conditions, the reaction proceeds by the dissociative adsorption of methanol onto a catalytic surface to form the methoxy radical. This is followed by the loss of a methyl hydrogen to form formaldehyde and water which desorb from the surface. The overall reaction is highly exothermic (ΔH=−156 kJ/mole) and can be written as in Equation 1:CH3OH+O→CH2O+H2O  Eq. 1
On Ag surfaces, the methanol-to-formaldehyde reaction is optimally run, in commercial operations, at temperatures between 800° K. to 900° K. The O2 molecules undergo dissociative adsorption, with the resulting high mobility oxygen atoms readily dissolving into the Ag bulk.
Previous efforts disclose the use of membranes to effect chemical reactions. U.S. Pat. No. 6,048,472 awarded to Nataraj, et al. on Apr. 11, 2000 discloses a process for the production of synthesis gas by permeating oxygen gas from one side of a mixed conducting membrane through to the other side where reaction occurs.
U.S. Pat. No. 5,430,210 awarded to Grasselli, et al. on Mar. 3, 1995 discloses a process for contacting, at reactive conditions, a hydrocarbon/hydrogen reactant feed stream with one side of a membrane and contacting the other side of the membrane with an oxygen stream.
U.S. Pat. No. 3,375,288 awarded to de Rosset, et al. on Mar. 26, 1968 discloses a process for withdrawing hydrogen from a product liquor so as to enhance yields in dehydrogenation reactions. The '288 patent maintains an oxygen-containing gas on one side of a silver membrane under pressure sufficient to cause oxygen to diffuse through the membrane. This oxygen supply is then utilized to combine with hydrogen to create water.
None of the aforementioned patents anticipate or suggest utilizing activated metal surfaces as a catalytic-type reaction site for oxygenation reactions. Rather, the prior art appears to be relegated to using membranes merely to separate reactant feeds from each other prior to reaction of one or several of the moieties in the feedstock streams.
A need exists in the art for a method for carrying out oxidation reactions at room temperatures. The method should utilize standard metal substrates and be conducted at pressures and temperatures lower than present commercial operations in order to cut operating costs. The method should keep pressurized reactant streams separate from each other to prevent explosions.